The Performance Evaluation of a Solar PV-Fuel Cell System Under Dynamic Irradiance and Temperature Conditions ^†

Abstract

Renewable energy sources (RESs) in microgrids are vital for sustainable and resilient power networks, especially in rural South Africa with diverse climatic conditions. Photovoltaic (PV) energy generation is intermittent, making it difficult to offer reliable electricity in varying conditions. The Proton Exchange Membrane Fuel Cell (PEMFC) and solar system are integrated in this study to provide a sustainable energy source that can address these issues. Under varying temperature and irradiance conditions, the PV system was evaluated with and without an LCL filter and PEMFC unit using PVGIS Northern Cape daily solar irradiation data. Results show that solar input variability causes large voltage fluctuations in the standalone PV system. This study adds to the expanding knowledge on RES resilience by utilising real-world climatic data and shows that PV-FC systems can be a sustainable and reliable option for microgrid and standalone applications in rural locations with ample resources or without electrical infrastructure.

1. Introduction

South Africa is dealing with substantial energy issues stemming from its reliance on coal-based power generation, which significantly impacts carbon emissions, pollution, and climate change, as demonstrated in Figure 1. The current energy mix is heavily dominated by coal, which constitutes 91.5%. In response, the government has established objectives to decrease this proportion to 59% by the year 2030 and to reach net-zero emissions by 2050 [1]. The increasing energy demand, especially in underserved rural areas, has prompted a significant transition towards renewable energy sources [2,3]. Solar photovoltaic (PV) systems stand out due to their scalability, cost-effectiveness, and positive impact on the environment. Nonetheless, the output from photovoltaic systems is fundamentally variable and significantly affected by changes in solar irradiance and surrounding temperature conditions. This variability presents a significant obstacle to ensuring a consistent power supply in standalone and microgrid applications.

Proton exchange membrane fuel cells (PEMFCs) present a complementary solution by effectively storing excess solar energy and providing power during periods of low irradiance or peak demand. The combination of PV systems with fuel cells can improve system reliability, energy independence, and environmental sustainability, especially in remote or off-grid situations [5]. Although they hold significant potential, PV-fuel cell hybrid systems have not seen widespread adoption in South Africa, and there is a scarcity of studies examining their dynamic performance in actual weather scenarios. Many investigations operate under the assumption of standard test conditions, failing to account for the operational challenges introduced by daily and seasonal fluctuations in solar irradiance and temperature.

This study aims to evaluate the dynamic performance of a standalone PV-fuel cell system under varying irradiance and temperature conditions, aiming to evaluate its feasibility for rural electrification through MATLAB/Simulink R2024b analysis. Data on empirical solar irradiance from designated regions in the Northern Cape, obtained from the Photovoltaic Geographical Information System (PVGIS), are employed to assess the dynamic performance of the system.

2. Overview of PV Systems and Fuel Cells

Solar energy denotes the portion of the sun’s heat radiation and light that may be captured at the Earth’s surface for diverse energy-generating purposes, particularly for the transformation of solar energy into usable energy forms. Solar cells are included within solar modules, formally known as PV modules. These PV solar modules, consisting of several cells containing photovoltaic material, are employed to generate power via the photovoltaic method [6,7]. Connecting electrical conductors to the positive and negative terminals of a circuit enables the harnessing of electrons to generate an electric current. The requisite power output can be attained by configuring several solar cells in series to elevate the voltage and in parallel to augment the current [8]. The equivalent circuit of a PV cell is shown in Figure 2. PV panels generate DC electrical energy contingent upon irradiance, temperature, and module specifications.

A variety of fuel cells (FCs) can be found in the current market. However, they are typically classified based on the type of electrolyte material or fuel they use. Their power outputs, operating temperatures, electrical efficiencies, catalysts used, and typical applications vary significantly [5]. The FC equivalent circuit is presented in Figure 3. The proton exchange membrane fuel cell (PEMFC) stands out as the optimal selection for fuel cells serving as a power source due to several compelling reasons:

• Reduced operational temperature, allowing for quick activation and deactivation;
• Decreased operational pressure, resulting in enhanced safety;
• Straightforward configuration into mode systems;
• Diminished emission ratio coupled with an improved conversion ratio [9,10].

Figure 3. PEMFC schematic and electrical circuit model [9].

Figure 3. PEMFC schematic and electrical circuit model [9].

3. The Impedance Source Inverter and Pulse Width Modulation Overview

The Z-source inverter (ZSI) utilises a unique impedance network to link the converter’s main circuit to the power supply, load, or another converter, offering specific benefits absent in traditional voltage-source (V-source) and current-source (I-source) converters, which rely on capacitors and inductors, respectively. The ZSI addresses the technical and scientific constraints of conventional V-source and I-source converters with the application of a new power conversion technology [11].

The ZSI operates as a buck-boost inverter, capable of functioning at various voltage levels. In contrast to Voltage Source Inverters (VSIs) and Current Source Inverters (CSIs), which are restricted to eight allowed switching modes, Z-Source Inverters (ZSIs) provide nine allowable switching modes, including the shoot-through (ST) state that facilitates voltage enhancement. The standard VSI forbids this ST zero state (or vector) because of the potential of a ST condition [11,12]. Figure 4 depicts the equivalent ZSI circuit.

The ZSI is connected to a load, another converter, or a DC supply by an X-arrangement of split-inductor L₁ and L₂ and capacitors C₁ and C₂. In most cases, the power switching components of switching devices such as IGBTs or MOSFETs are utilised in the ZSI. MOSFETs are employed in the ZSI, and they promise to use simpler and more efficient drive circuits, with substantial savings in costs over bipolar devices [12].

The simple boost control (SBC) method is regarded as the fundamental approach for ZSI topology that is employed for switching the MOSFETs or IGBTs of the universal bridge, such that the endpoints of a ZSI that generate the desired AC output waveform. It entails comparing three-phase reference signals (V_a, V_b, and V_c) with a carrier signal for non-shoot through operation of the inverter, along with two straight shoot through (ST) lines (V_p and V_n) compared to the carrier for ST operation of the inverter, as illustrated in Figure 5. The dashed vertical lines in Figure 5 represent switching borders during each modulation cycle, whereas the black shaded intervals indicate ST states purposefully produced during PWM operation to enhance DC-link voltage. The ST state happens when any of the seven ST states discharge the Z-source impedance terminals. The Z-source network is cut off by connecting both switches in any leg of the bridge simultaneously [12]. The non-ST state occurs when the ZSI is in one of the active or zero states (such as a typical VSI) for an extended period. When the diode is forward-bias, the capacitors begin to charge, and the power stored in the inductors gets distributed to the load [12]. When the Z-source network is in its shoot through state, the diode opens and the bridge is equivalent to a short-circuit, while in the non-ST state, all eight switches are active [14].

4. The LCL Filter Overview

The installation of a suitable high-inductance filter efficiently mitigates harmonics in DC-AC converters [15]. The substantial size of the inductor makes inductive filters too costly for practical applications beyond several kilowatts, despite their simple design, and they demonstrate insufficient dynamic responsiveness [15]. The ZSI application necessitates a low-pass filter to transmit low-frequency components while attenuating high-frequency harmonics [12]. Figure 6 illustrates the schematic representation of a typical LCL filter. The LCL filter exhibits a positive response to current ripple, even with the use of low inductance. LCL offers enhanced decoupling of the circuit from the grid, surpassing the performance of the other two filters in terms of loss characteristics. The attenuation of the LCL filter is roughly -60 dB per decade [12,15,16].

5. The 55 kW PV System Modelling and Design

5.1. Environmental Input Parameters

This study employed actual daily irradiance data for January sourced from the PVGIS database to simulate realistic operating conditions, concentrating on the Northern Cape province, recognised for its significant solar potential and extreme temperature fluctuations as shown in Figure 7. The selected values aim to assess the dynamic performance of the hybrid system amidst actual variations in solar availability and thermal operating conditions.

5.2. PV Array Design Parameters

The PV array was constructed utilising Canadian Solar CS6U-345M polycrystalline modules. A configuration of nine modules in series, along with 18 parallel strings, was established to produce a maximum output of 55 kW. The specifications of the panel are summarised in

Table 1. CS6U-345M Polycrystalline PV solar panel parameters.

Parameter	Value
Maximum power	345.186 W
Open circuit voltage (VOC)	46.4 V
Short circuit current (ISC)	9.56 A
Voltage at maximum power point (Vmp)	38.1 V
Current at maximum power point (Imp)	9.06 A

; the array voltage is 342.9 V, while the DC link voltage is set at 514.35 V.

5.3. ZSI and LCL Filter Design Parameters

This PV system converts DC to AC in one step using a ZSI. The inverter converts DC to AC efficiently using multilayer PWM and MOSFETs to generate low harmonic distortion output. The selected SBC controls the MOSFET shoot-through condition and ZSI output voltage, which are crucial for inverter performance. An LCL filter improves ZSI output voltage waveforms and reduces system harmonics.

Table 2. The ZSI and LCL filter parameters.

Parameter	Value
L1 = L2 of the ZSI	43.805 µH
C1 = C2 of the ZSI	88.072 µF
PPV	55.95 kW
Switching frequency for ZSI (fsw)	20 kHz
Duty cycle (D)	17%
L1 of the filter	269.57 µH
L2 of the filter	1.673 µH
C of the filter	741.664 µF
Switching frequency for the LCL filter (fsw)	10 kHz

shows ZSI and LCL filter design parameters.

6. The System Results

6.1. Voltage Waveforms Before Filtering

Early-stage irradiance supplies minimal energy, keeping system voltage around zero for 0–5 s (early morning). Voltage increases at 5–10 s (morning), peaking 10–15 s (midday) into the observation time. The PV array’s irradiance or power output increased during the simulation. High-frequency oscillations and voltage ripples occur during voltage increase and decrease. Poor filtering and dampening cause oscillations in Figure 8.

The PEMFC was added to the system. Figure 9 shows that the PEMFC alone powers the microgrid even after 20 s (afternoon) of lower PV array irradiation than Figure 8. Comparing 800 V to the converter’s DC link’s 514.35 V reveals an increase.

6.2. Voltage Waveforms After Filtering

The performance voltage profile in Figure 10 now has a smoother sinusoidal waveform with reduced ripple, notably at peak irradiance between 10 and 15 s (midday). The LCL filter reduces inverter switching harmonics, enhancing voltage. The voltage profile shape is improved, although magnitude shifts occur between the beginning (10–15 s) and end (20 s) transitions. These oscillations are caused by insufficient energy backup and variable irradiance.

Figure 11 shows that PEMFC delivers energy and stability above PV under a 30 s (mimicking a day) simulation that stabilises the waveform. Despite irradiance changes, the voltage waveform stabilises after 10 s. PEMFCs provide smooth transitions and reduce voltage fluctuation during irradiance drop-off while delivering energy.

6.3. PV-PEMFC System Performance

PEMFC integration stabilises PV power output, and LCL filtering improves waveform quality and load voltage. The hybrid arrangement suppresses transient oscillations, increasing power quality in this system, as shown by the 74% ripple reduction from Figure 12. These findings demonstrate that LCL filtering reduces harmonic content, ensuring inverter output standards.

6.4. PEMFC Stack Voltage

PEMFC voltage is low for the first 0–5 s. In the simulation, especially around 5–10 s, the voltage rapidly rises to meet the rising energy needs that the PV system alone cannot supply, as shown in Figure 13. The PEMFC quickly boosts voltage to stabilise the system. The PEMFC outputs 400 V for 10–20 s. During peak operation, the PV system receives maximum irradiance. Small voltage ripples indicate a dynamic response to load and PV output fluctuations. The voltage drops after 20 s and stabilises at 250–300 V. When nighttime solar irradiance drops, system demand drops or PV contribution rises. The PEMFC cuts output to conserve energy and boost efficiency. Dynamically responsive PEMFC voltage fluctuations are smooth and regulated. It matches its output to the PV system to give electricity during solar input changes.

7. Conclusions

This study detailed the design, modelling, and performance assessment of a solar PV–PEMFC system under varying solar irradiance and temperature conditions, utilising daily irradiance data from the Northern Cape area of South Africa. The main objective was to examine the efficacy of combining a PEMFC with a PV system to improve energy stability and quality in microgrid applications. The integration of the PEMFC resulted in a notable improvement in voltage stability and power supply continuity within the solar PV-PEMFC system. The PEMFC compensated for intermittent PV system production, notably during low irradiance times, to ensure a more constant voltage output. Additional future work will explore this system under diverse climatic profiles to evaluate seasonal adaptability.